Method of grading copper for use in



Patented Apr. 15, 1952 METHOD OF GRADING COPPER FOR USE IN COPPER OXIDE RECTIFIERS Herbert L. Taylor, Turtle Creek,

Pa., assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania No Drawing. Application March 31, 1949, Serial No. 84,765

14 Claims. (Cl. 23230) My invention relates to the manufacture of copper oxide rectifiers, and particularly to a method of testing commercial electrolytic copper to determine its suitability for use in the manufacture of such rectifiers.

There are three principal characteristics by which the performance of copper oxide rectifiers are judged. These are the rectifying ratio, the forward resistance stability, and the reverse resistance stability. The rectifying ratio may be defined as the ratio between the forward resistance measured under specified conditions and the reverse resistance, usually measured under different specified conditions. The forward resistance stability is concerned with the variations in forward resistance of the rectifier over a period of time, usually at least a year, following its manufacture. The reverse resistance stability is similar. The term forward resistance is used to describe the resistance of the rectifier to current flow in the low resistance direction and the term reverse resistance is used to describe the resistance of the rectifier to current flow in the high resistance direction.

It is well known that rectifiers produced by the same process from different samples of copper vary widely in respect to these three characteristics. The cause of this variation is not known, but it is commonly attributed to the pres ence of minute quantities of impurities whose exact nature has not been determined. It is known that the quality of rectifiers varies with the source of the copper, that is, copper from one mine will consistently produce good rectifiers, whereas copper from a different mine will consistently produce poor rectifiers. It is also known that copper from the beginning of the pour from the smelter will produce better rectifiers than copper from the end of the pour.

It is relatively easy to determine in advance whether or not a given batch of copper will prouce rectifiers having a suitable rectifying ratio.

This is commonly done by making a rectifier from a sample of the batch of copper and measuring its rectifying ratio. The stability of the forward and reverse resistance characteristics are more diificult to determine because of the time requirement involved, and it has consequently been customary to rely on previous experience in selecting copper for the manufacture of rectifiers to insure that the stability characteristics of the finished rectifiers will be satisfactory.

It is an object of my invention to provide a testing method which may be readily and quickly performed and which will indicate the suitability of a given sample of commercial electrolytic copper for the manufacture of copper oxide rectifiers.

A further object is to provide a test of the type described which Will indicate the reverse resistance stability characteristics of a rectifier produced from a sample or commercial electrolytic copper whose rectifier characteristics are unknown.

I accomplish the foregoing and other objects of my invention by making a copper oxide rectifier from a sample of the copper to be graded. In making the test rectifier, I give the copper blank a preoxidation rinse in a solution containing iodine or an iodide. I have found that such a preoxidation rinse affects the adherence of the oxide to the copper. The iodine solution used has a concentration which is determined by actual test and which has a known oxide flaking effect when applied as a preoxidation treatment to copper having known rectifier characteristics. After being treated with such a solution, the copper sample having unknown rectifier characteristics is oxidized and the degree of adherence of the oxide coating to the copper is then observed. If the oxide coating flakes off as readily or more readily than from the known copper, then the reverse resistance stability characteristics of the unknown copper sample are equal to or better than those of the known copper. If the oxide coating does not flake off, then the reverse resistance stability characteristics of the unknown sample are poorer than those of the known copper.

I shall describe several processes embodying my invention, and shall then point out the novel features thereof in claims.

I have found that if an iodine containing solution is employed as a preoxidation rinse in the manufacture of a copper oxide rectifier, it may cause the oxide coating to flake readily away from the copper after the oxidation process has been carried out. The flaking depends upon the particular solvent and solute selected, and upon the concentration of the solution. I have found that the better the reverse resistance stability of a copper sample, the weaker the iodine solution that will cause its oxide coating to flake oil when the solution is applied as a preoxidation treatment.

To grade copper for use in copper oxide rectifiers, it is necessary to determine whether a sample of copper whose rectifier characteristics are unknown has a reverse resistance stability equal to that of another copper, of which samples are available and whose rectifier characteristics have been proven by experience.

Before proceeding with a test in accordance with my invention, the copper samples should be cleaned by treatment with a suitable cleaning solution. For example, the samples may be cleaned in a solution of 50% normal nitric acid. The cleaning solution is then removed from the samples, preferably by rinsing them several times in distilled water.

I then grade the unknown copper by carrying out my invention in the following manner. I first determine the minimum strength of iodine containing solution which will cause oxide flaking when applied as a preoxidation rinse to a sample of the copper whose rectifier characteristics are known. This maybe done by preparing a series of iodine containing solutions having different concentrations of iodine. Each one of a series of samples of the copper having known rectifier characteristics is treated withone of this series of solutions. After this treatment, the samples are dried and are then immediately oxidized so as to form an oxide coating on the copper. After the oxidation process, the cop per sample is, cooled and the degree of adherence of the; oxide coating to the copper is observed. The solution of lowest concentration of iodine which caused the oxide to flake off is the one selected as the solution for treatment of the copper sample having unknown rectifier characteristics.

' That sample is then given a prexoidation treatment in the selected solution and is then dried, oxidized, and cooled. Thedegree of ad- I herence of the oxide coating to the copper is then observed. An oxide coating which adheres better than the coating of the known sample tested with the same solution indicates a poorer grade of copper for rectifier purposes. On the other hand, a coating which flakes off readily indicates an equal or better grade of cOpDer.

Several different iodine containing solutions may be used successfully in this process. For example, I have used solutions of iodine crystals in water and in alcohol. I have also used water solutions of various iodides, including the iodides of hydrogen, sodium, potassium, copper, and iron (ferrous). The particular solvent used is apparently not critical. It is believed that any solvent may be used which will dissolve the selected iodine containing substance, so long as it has no adverse effect on the copper.

The temperature of the iodine containing solution is not critical. The process works well with solutions at room temperatures in the neighborhood of C.

Variations in the flaking effect on copper oxide may be observed only in relatively dilute solutions of the iodine containing'compound. The range of concentration of iodine varies with the particular solvent and the particular solute selected. The following ranges of concentration have been found to be suitable: Iodine in water, 3.4 to 34 parts iodine per million parts water; iodine in alcohol, 3.6 to 36 parts iodine per million parts alcohol; hydriodic acid, 3.58' to 35.8 parts iodine per million parts water; sodium iodide, 18 to 4000 parts iodine per million parts water; potassium iodide, 18 to 4000 parts iodine per million parts Water; copper iodide, 3.55 to 5.32 parts iodine per million parts water; ferrous iodide, 3.6 to 15 parts iodine per million parts water.

The concentration limits given immediately above are approximate only. The lower limit in each case represents the lowest concentration which has been found to cause oxide flaking on the best known copper sample. The upper limit of concentration shows the greatest concentration which has caused the flaking of oxide from the lowest quality copper so far tested. It appears possible that for coppers of better or worse qualities than those which have been tested,

concentration limits different from those given above, would be obtained.

The time of the preoxidation treatment does not appear to be critical. Immersion of the copper samples in the test solution for a period of 30 seconds gives satisfactory results.

After the preoxidation treatment, the copper samples should be dried and the oxidation treatment started as soon as possible. Any delay of more than two hours at this point of the process seriously reduces the sensitivity of the test.

Any of the well-known oxidation processes may be used. In a typical process, the blanks are oxidized in air at a temperature'in the neighborhood of 1030 C. for approximately 13 minutes, and. are then cooled in air to a temperature in the neighborhood of 550- C. The oxidized blanks are annealed at substantially the latter temperature for approximately 10 minutes, afterwhich they are quenched in running tap water.

The number of copper samples beingtested should be small as compared to the capacity of the oxidation furnace. It has been found that if the furnace is crowded, the sensitivity of the test is adversely afiected.

The water quench after the annealing is; not necessary, as it does not affect the sensitivity of the test, and it does permit more rapid observationof the test results.

Many tests to determine reverse resistance stability characteristics of rectifiersaccording to the foregoing description have now been checked by. actual aging tests of rectifiers produced from the same copper. In every. instance where commercial electrolytic copper was. used, the actual aging. test has substantially confirmed, the results, predicted by the test described above.

Although. I, have herein shown. and. described several processes of. grading. commercial electrolytic copper for use in, copper oxide; rectifiers embodying, my invention, it. is, understood, that various changes. and. modifications, may be made therein. within. the scope of the, appended claims Without departing from the spirit and scope ofmy invention.

Having; thus described my invention, whatI, claim is:.

1. The method of grading, copper for use. inmanufacturing copper oxide rectifiers which comprises the steps of treating a sample-ofthe copper to be graded with a. solution. containing iodine having, a, known oxide flaking effect whernapplied as, a preoxidizing treatmentto a. similar sample of copper-having known rectifier. characteristics when oxidized to form an. oxide film. thereon; heating the treated sample in, an oxidiz n at,- mosphere to form an oxide coating thereon; and cooling the oxidized sample, the degree, of flaking of the oxidecoating of the treated copper sample following the cooling step being. indicative of the rectifier characteristics.

2. The method of grading copper for use in. manufacturing copper oxide rectifierswhichcomprisesthe steps of treating a sample of the copper to be graded with a solution containing iodinein a concentration having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier characteristics when oxidized to form an oxide film thereon, heating the treated sample in an oxidizing atmosphere to form an oxide coating thereon, and quenching the oxidized sample, to induce by such treatment flaking of the oxide coating which if occurring indicates that a rectifier prepared from said sample by standard procedures will have characteristics superior to a predetermined norm and by an amount related to the degree of such flaking.

3. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating a sample of the copper to be gradedwith a solution containing iodine in a concentration having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier characteristics when oxidized to form an oxide film thereon and comprising a solute selected from the group consisting of iodine, hydriodic acid, sodium iodide, potassium iodide, ferrous iodide and copper iodide and a solvent selected from the group consisting of water and alcohol; heating the treated sample of copperin an oxidizing atmosphere to form an oxide coating thereon; and cooling the oxidized sample of copper, the degree of flaking of the oxide coating of the treated copper sample following the cooling step being indicative of the rectifier characteristics.

4. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating a sample of the copper to be graded with a water solution containing iodine in a concentration having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier characteristics when oxidized to form an oxide film thereon and selected from the group consisting of a solution of iodine crystals in Water containing approximately from 3.4 to 34 parts iodine per million parts water, a hydriodic acid solution containing approximately from 3.58 to 35.8 parts iodine per million parts water, a sodium iodide solution containing approximately from 18 to 4000 parts iodine per million parts water, a potassium iodide solution containing approximately from 18 to 4000 parts iodine per million parts water, a copper iodid solution containing approximately from 3.55 to 5.32 parts iodine per million parts water, and a ferrous iodide solution containing approximately from 3.6 to parts iodine per million parts water; heating the treated sample of copper in an oxidizing atmosphere to form an oxide coating thereon; and cooling the oxidized sample of copper, the degree of flaking of the oxide coating of the treated copper sample following the cooling step being indicative of the rectifier characteristics.

5. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating a sample of the copper to be graded with a solution of iodine in alcohol in a concentration having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier characteristics when oxidized to form an oxide film thereon, heating the treated sample of copper in an oxidizing atmosphere to form an oxide coating thereon; and cooling the oxidized sample of copper, the degree of flaking of the oxide coating of the treated copper sample following the cooling step being indicative of the rectifier characteristics.

6. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating a sample of the copper to be graded with a solution of iodine in water in a concentration having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of'copper having known rectifier characteristics when oxidized to form an oxide film thereon, heating the treated sample of copper in an oxidizing atmosphere to form an oxide coating thereon; and cooling the oxidized sample of copper, the flaking off of the oxide coating from the treated sample as readily or more readily thanfrom the copper of known characteristics following the cooling step indicating that the rectifier characteristics of the treated sample are equal to or better than those of the copper of known characteristics.

'7. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating a sample of the copper to be graded with a solution of hydriodic acid in Water in a concentration having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier characteristics when oxidized to form an oxide film thereon, heating thetreated sample of copper in an oxidizing atmosphere to form an oxide coating thereon; and cooling the oxidized sample of copper, the degree of flaking of the oxide coating of the treated copper sample following the cooling step being indicative of the rectifier characteristics.

8. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating a sample of the copper to be graded with a solution of sodium iodide in water in a concentration having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier characteristics when oxidized to form an oxide film thereon, heating the treated sample of copper in an oxidizing atmosphere to form an oxide coating thereon; and cooling the oxidized sample of copper, the degree of flaking of the oxide coating of the treated copper sample following the cooling step being indicative of the rectifier characteristics.

9. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating a sample of the copper to be graded with a solution of potassium iodide in water in a concentration having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier characteristics when oxidized to form an oxide film thereon, heating the treated sample of copper in an oxidizing atmosphere to form an oxide coating thereon; and cooling the oxidized sample of copper, the degree of flaking of the oxide coating of the treated copper sample following the cooling step being indicative of the rectifier characteristics.

- 10. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating a sample of the copper to be graded with a solution of approximately from 3.6 to 36 parts iodine per million parts alcohol having a known oxide flaking effect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier characteristics when oxidized to form an oxide film thereon, heating the treated sample of copper in an oxidizing atmosphere to form, anoxide coating thereon; and coolingthe oxidized sample of copper, the degree of. flaking ofthe oxide coating of the treated copper. sample following the cooling step being: indicative. of the rectifier characteristics'.

11. The method of grading copper ior use in manufacturing copper oxide rectifiers which comprises the steps of treating. a. sample; of the; copper to be graded with a solution oi approxk mately from. 3A to 34: parts; iodine per: million parts water having a known oxide flaking efiect when applied as a preoxidizing treatment to a similar sample of copper having known rectifier' characteristics: when. oxidized to form an oxide film thereon, heating the. treated sample of copperin' an oxidizing, atmosphere. to form an oxide. coating thereon; and cooling the oxidized sample of copper, the degree of flaking of the oxide coating of the treatedcopper sample following the cooling step being indicative of the rectifier characteristics.

12. The method of grading copper for use in manufacturing copper oxide rectifiers which comprises the steps of treating: a sample. of the copper to be graded with aisolutionof hydriodic acid in water and containing approximately from 3.58 to 35.8 parts iodine per million parts water having a known oxide flaking effectwhen applied as a preoxidizing treatment to a similar sample of copper having: known. rectifier characteristics when oxidized to form an oxide film thereon, heating the treated sample of copper in an oxidizing atmosphere to form anoxide coating thereon; and cooling the oxidized sample of copper, the degree of flaking of the oxidecoatin of the treated copper sample following the cooling step being indicative of the rectifier characteristics.

13-. The method of grading copper for use in manufacturing: copper oxide. rectiflers which comprises the steps of treating a sample of the copper; to be graded with a, solution, of sodium.

ing of the treated copper sample following. thecooling step being indicative of the rectifier characteristics.

14 The method of grading copper for use in manufacturing copper oxide rectiflers which comprises the steps of treating a sample of the copper to be graded with a solution of potassium iodide in water and, containing approximately from 18 to 4000 parts iodine per, million parts water having a known oxide flaking effect when applied as a preoxidizing treatment to. a similar sample of copper. having; known rectifier characteristics when oxidized to form an oxide film thereon. heating the treated sample of copper in an oxidizing atmosphere to form anoxide coating there-- on; and cooling the oxidized sample of copper, the; degree of, flaking of the oxide coating of the treated copper sample following the cooling step being indicative: of the rectifier characteristics.

HERBERT L. TAYLOR.

No references cited. 

1. THE METHOD OF GRADING COPPER FOR USE IN MANUFACTURING COPPER OXIDE RECTIFIERS WHICH COMPRISES THE STEPS OF TREATING A SAMPLE OF THE COPPER TO BE GRADED WITH A SOLUTION CONTAINING IODINE HAVING A KNOWN OXIDE FLAKING EFFECT WHEN APPLIED AS A PREOXIDIZING TREATMENT TO A SIMILAR SAMPLE OF COPPER HAVING KNOWN RECTIFIER CHARACTERISTICS WHEN OXIDIZED TO FORM AN OXIDE FILM THEREON; HEATING THE TREATED SAMPLE IN AN OXIDIZING ATMOSPHERE TO FORM AN OXIDE COATING THEREON; AND COOLING THE OXIDIZED SAMPLE, THE DEGREE OF FLAKING OF THE OXIDE COATING OF THE TREATED COPPER SAMPLE FOLLOWING THE COOLING STEP BEING INDICATIVE OF THE RECTIFIER CHARACTERISTICS. 